Propylene glycol: the humectant feared as antifreeze
Arin Editorial · how this is made
When you see propylene glycol on a cosmetic label, you might think of car antifreeze. It really is used in fluids that keep airplanes and cars from icing. Yet the same substance has been used for years in food and medicine, not just cosmetics.
What is propylene glycol?
Propylene glycol is a diol with two alcohol groups, also known as 1,2-propanediol. It is colorless, odorless and slightly sweet. Its main jobs are holding moisture, dissolving ingredients and maintaining texture. You will find it in creams, shampoos, cleansers and deodorants.
Don't confuse it with ethylene glycol
Ethylene glycol, the one people think of as antifreeze, is toxic and not used in cosmetics. Propylene glycol is described as a low toxicity compound and is used as a food additive and drug carrier. Treating them as the same is the most common mistake.
What scientific records say
EPA's compilation lists propylene glycol as 'not likely to be carcinogenic to humans'. Lab screens looking for estrogen receptor activity did not find an effect. Genotoxicity tests are mixed: some positive, some negative, so there is no clear evidence of genetic damage. Skin irritation studies showed no significant irritation.
Why it gets attention
Two things fuel the worry. One is the 'antifreeze in cosmetics' phrase; the compound is used industrially, but its cosmetic purpose and dose differ. The other is a 2010 indoor air study linking propylene glycol and glycol ethers in bedroom air to respiratory and immune problems in children. That association is not proof of causation, and e-cigarette liquids add another debate.
Current regulatory status: EPA classifies propylene glycol as 'not likely to be carcinogenic to humans', and its cosmetic use is covered by independent panel reviews such as CIR.
If you see propylene glycol on a label, there is no need to throw the product away. For sensitive skin, patch test on the inner arm or behind the ear; stop if it stings or reddens. Knowing that the purpose and dose in cosmetics differ from industrial antifreeze should ease the worry.
Sources
- EPA ToxCast / ToxValDB (CompTox Chemicals Dashboard) - CAS 57-55-6
- Cosmetic Ingredient Review: Safety Assessment of Propylene Glycol, Tripropylene Glycol, and PPGs as Used in Cosmetics
- 2010 indoor air quality study on propylene glycol ethers